This section provides background information to facilitate a better understanding of the various aspects of the disclosure. It should be understood that the statements in this section of this document are to be read in this light, and not as admissions of prior art.
In conventional power transmission belts, the belt has an inner compression section, an outer tension section, and an intermediate neutral plane. Typically, helically wound reinforcing cords are located within the neutral plane and so the neutral plane is commonly referred to as the load carrying zone. Such belts have a variety of groove and rib configurations, using longitudinal or transverse grooves/ribs or a combination of both. The grooves are often located in the inner compression section of the belt. The grooves assist in engaging a pulley, or other drive, in the power transmission system. For some belts, grooves and rib configurations may also be provided in the outer tension section.
The generation of adhesion between the reinforcing cords and rubber compounds within the neutral plane and adjacent thereto, in dynamic products such as belts, tires, couplings, or hose is fundamental to their proper operation. Without sufficient adhesion, the product will fail to perform under dynamic conditions. An adhesive system may include many components or layers beginning with a fiber sizing applied to the fibers as they are spun, a primer typically applied to a yarn or greige cord or fabric or other fibrous reinforcement, an adhesive applied to and/or within the cord, and an overcoat applied to the treated cord bundle (or other fibrous reinforcement) to ensure compatibility with the surrounding rubber compound. The treated cord may finally be embedded in or surrounded by an adhesive or gum type rubber composition generally formed from one or more rubber plies or layers making up the body of the belt or other dynamic rubber product.
A conventional treatment for reinforcing cords consists of three coatings: 1) a primer treatment of isocyanate or epoxy in organic solvent; 2) a resorcinol-formaldehyde-latex (“RFL”) treatment; and 3) a conventional overcoat adhesive based on a complex blend of chlorinated polymers, curatives, crosslinkers, adhesion promoters, film-formers, and/or acid scavengers, and the like. In some cases, a variation used for aramid cord includes a first polyurethane treatment based on hydroxyl- or epoxy-terminated liquid rubber and isocyanate-terminated liquid rubber, either of which may be a diene rubber, followed by a conventional RFL treatment. Presumably, an overcoat adhesive would also be needed for many applications, such as for bonding to ethylene-alpha-olefin rubber compounds. These are a complex series of treatments that are expensive, may involve some environmentally unfriendly components, and require optimization for best performance.
Developments in the automotive industry have resulted in higher engine output in a more compact engine compartment. As a result, power transmission belts useful for such engines have been required to operate under increasing loads, at even higher tensions, and at high temperatures while reducing belt width. This environment demands a high quality belt capable of withstanding these severe conditions, but which is prepared by less complex processes. Some ways to improve the properties of such belts has been to improve the materials from and techniques by which the belts are made.